In recent years, according to an increase in an amount of data handled in a company, a storage apparatus includes a large number of storage devices and the capacity of the storage device also increases year after year. As the storage device, in general, a HDD (Hard Disk Drive) is mounted. However, in recent years, instead of the HDD, a storage device (e.g., an SSD: Solid State Drive) including a nonvolatile semiconductor memory (e.g., a flash memory) as a storage medium attracts attention. The SSD is expensive but is extremely fast in I/O processing compared with the HDD.
In the flash memory, a physical storage area is managed in units called blocks. Erasing of data is performed in the block units. There is an upper limit in the number of times the block can be erased. When the number of times of erasing increases, data sometimes cannot be written in the flash memory or an error occurrence ratio of data written in the flash memory sometimes increases. That is, the flash memory has the life and the SSD including a large number of flash memories also has the life. In the flash memory, in general, fluctuation occurs in quality in units of dies, chips, or the like. A low-quality die is made unusable by a failure even if the number of times of erasing is smaller than a predetermined number of times of erasing. When such a failure occurs in a plurality of dies, a storage area for storing user data cannot be secured and the storage device has to be closed. When the SSD becomes unusable earlier than a predetermined period in this way, it is likely that the frequency of replacement increases and costs for purchase and maintenance of the SSD are incurred.
For example, PTL 1 discloses a technique for restoring data when a failure occurs in a block in an SSD. There is known a technique for rebuilding, when a failure of a block in a certain SSD is detected in a storage apparatus including a plurality of SSDs, all data of the SSD including the failure block in another SSD.